Phenomenal Cosmic Power

HORRIBLE NEWS, EVERYONE! - "All Rank 4 Essences can no longer be earned once Shadowlands strikes" -- As of 9.0.2 this now seems to be in effect.

This achievement required you to get rank 4 of all of a role’s Essences that were released in the Rise of Azshara update (patch 8.2). It did not include any of the new Essences in 8.3.

Assuming you had already gotten all rank 3s, you were required to do all the below steps:

Get your neck to lvl 70,
Get your 3 Nazjatar bodyguards all to rank 30,
Get RNG lucky with Rustbolt Paragon chest,
Get RNG lucky with Nazjatar rep Paragon chest,
Get RNG lucky with the weekly Island Expedition treasure map quest,
Get 25 PvP supply chests in Nazjatar as an assassin,
Get 100,000 Honor points in instanced PvP,

Complete Operation: Mechagon Hard Mode with 0 deaths,
Kill Queen Azshara on Mythic Difficulty,
Reach Elite rank (2400) in BFA PvP season 3 or later,
Complete every Mythic+ dungeon In Time at M+15 or above in BFA season 3 or later.

It's theoretically still obtainable if someone attained the required Rank 4 items before 9.0.2 but never used them, otherwise this is no longer obtainable.

azeroths neckbeard

... Itty-bitty living space